Some activities ("restricted activities") at a construction, mining or similar site are sufficiently hazardous that site personnel and equipment are excluded from, or the associated activities are constrained within, a region, referred to here as a buffer zone, that surrounds the location(s) where the restricted activity occurs. If the restricted activity is more or less continuous and the location or activity site where the restricted activity occurs is fixed or stationary, a permanent buffer zone can be defined and imposed surrounding the restricted activity site. However, many hazardous activities occur only over a limited time interval and/or the restricted activity site may move with time. For example, a truck delivering potentially unstable explosives may move (slowly) across a construction or mining site to a location where the explosives will be used. In this situation, it may be preferable to define a buffer zone that is not fixed but can vary with time.
Creation of, or prediction of locations for, stationary exclusion zones and the like, that control access to a specified area, are disclosed in several U.S. Patents. However, these exclusion zones, once created, do not move or undergo changes in size or other characteristics. Such an exclusion zone may be appropriate for a fixed structure, such as a building, with a fixed function that gives rise to the exclusion; but creation of such a zone would be of little help where the structure moves or the zone itself appears and disappears, or undergoes a change in size or other characteristics or a change in priority of an activity associated with the structure, with the passage of time.
What is needed is a system for creating and subsequently monitoring a variable buffer zone whose location, size and/or character can change with time to correspond to the location, size, priority and nature of a potential threat of a restricted activity site located within a larger site, such as a construction or mining site. The variable buffer zone (1) is activated at a fixed location but only for a limited time interval or (2) is activated in a region whose size and/or location changes with time or (3) corresponds to a restricted activity whose nature changes with time. Preferably, the system should permit the buffer zone size to vary according to the type and hazard level of the restricted activity. Preferably, the system should permit assignment of priority indices and/or hazard indices to activities and should allow the possibility that one or more high priority activities are permitted to continue within an activated buffer zone, while other lower priority activities are constrained or stopped altogether. Preferably, the system should permit transmission of indicia that define or otherwise describe the location, size or status of the buffer zone as time changes and should facilitate receipt and use of this information by a central system and by autonomous information-receiving units carried by persons, vehicles and other movable and non-movable structures on or near the site. Preferably, the system should allow for possible overlap of activated buffer zones.